单点触摸产生波纹（类似水波）

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package com.zking.diypointtouch;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.os.Handler;import android.os.Message;import android.view.MotionEvent;import android.view.View;/** * Created by Administrator on 2017/7/9 0009. */public class Practice extends View{    //画笔    private Paint mpaint;    //定义圆线的宽度    private int mstroken;    //圆心    private int cx;    private int cy;    //半径    private int cr;    //发送消息    private static final int FLUSH=0;    public Practice(Context context) {        super(context);        init();    }    private void init(){        //初始化画笔        mpaint=new Paint();        //抗锯齿        mpaint.setAntiAlias(true);        //设置颜色        mpaint.setColor(Color.BLACK);        //设置圆线的宽度        mpaint.setStrokeWidth(mstroken);        //设置圆的透明度        mpaint.setAlpha(255);        //初始值        mstroken=0;        cr=0;    }    @Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        canvas.drawCircle(cx,cy,cr,mpaint);    }    @Override    public boolean onTouchEvent(MotionEvent event) {        // 判断手势按下和抬起        switch (event.getAction()) {            case MotionEvent.ACTION_DOWN:                cx = (int) event.getX();                cy = (int) event.getY();                break;        }        // 初始化        init();        // 发送        handler.sendEmptyMessage(FLUSH);        return true;    }    private void flush(){        cr+=10;//每次都加十        mstroken=cr/4;//圆线的粗细        mpaint.setStrokeWidth(mstroken);//重新设置        int nextAlpha=mpaint.getAlpha()-20;//每次减20        if(nextAlpha<0){//避免透明度为负           nextAlpha=0;        }        mpaint.setAlpha(nextAlpha);    }    private Handler handler=new Handler(){        @Override        public void handleMessage(Message msg) {            switch (msg.what) {                case FLUSH:                    flush();                    invalidate();//重新绘制                    if (mpaint.getAlpha() != 0) {                        //每100ms刷新一次                        handler.sendEmptyMessageDelayed(FLUSH, 100);                    }                    break;            }        }    };}
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